Drives for mold closing systems and calibration blow mandrel systems in blow molding machines on one hand need to be capable of performing fast movements in order to facilitate a rapid opening of the mold in connection with a swift removal of the molded article. On the other, they have to be able to apply, for a period of up to tens of seconds, the high forces required during the blow molding process. Currently, either hydraulic cylinders or several electric motors are employed for this purpose.
Hydraulic cylinders, abeit meeting the aforementioned requirements, are highly energy-intensive, require regular and laborious maintenance, are not suited for cleanroom production and feature a low level of positioning accuracy.
Even though electric motors do not suffer the same shortcomings, one and the same electric motor cannot deliver both, fast movements and high forces. It is for this reason that known electromechanical drives in blow molding machines utilize two separate electric motors: While a first “fast and weak” motor is active during a first phase of the movement, characterized by fast motion at a low force, a second “slow and strong” motor actuates during a second phase, characterized by slow motion at a high force (see DE 199 32 741 A 1, DE 102 53 555 B3 and DE 200 15 590 U 1). However, construction and control of these two-step electromechanical drives feature a high degree of complexity, giving rise to an elevated risk of faulty operation as well as high production costs.